Cathode insulator



June 9, 1953 E. POHLE 2,641,727

CATHODE INSULATOR Filed May 24, 1950 INVENTOR. ERIC POHLE A TTORNE'YS Patented June 9, 1953 CATHODE INSULATOR Eric Pohle, Clifton,'N. J., assignor a Allen 3..

Du Mont Laboratories, Inc Clifton, N. J., a

corporation of Delaware Application May 24, 1950, Serial No. 163,981

is in normal use, the undesirable leakage path between the cathode and grid frequently forms on the surfaceof this disk insulator by the evaporation of metal from the outerwalls of the cathode cylinder. I As more and more metal is deposited on thedisk, a conductive film is built up which forms an electrical connection between the cathode and grid and ruins the'tube.

It is one object of this invention to provide an improved cathode ray tube by providing an insulating disk on which a continuous film between the grid and cathode cannot form.

' Another object is to provide a cathode support insulator which, without the assistance of other, complicated structures, will prevent the formation of the continuous conductive film between grid and cathode.

Other objects and advantages will in part be obvious and in part appear hereinafter.

The invention is accordingly embodied in a cathode structure for an electron emission device in which that portion thereof which evaporates metal which tends to deposit on insulation intervening between the cathode and control grid is modified to provide a shadow zone surrounding the cathode structure so that metal evaporating from surfaces in the cathode structure and passing in straight lines to theinsulator will not see the shadow zone. Briefly the invention isbased on the observation that evaporating metal will travel in relatively straight lines to the nearest relatively cool surface to condense and, accordingly, by incorporating in the insulator of a cathode structure a shadow zone the formation of a continuous conductive metal film on the insulator is avoided. The invention thu is embodied in a 6 Claims. (01. 313-250) Figures 3, 4 and 5 show different embodiments of this invention. I I

In Figure. 1 the cathode, comprising a cylindrical sleeve I I having'a cap I2 welded or otherwise secured thereto, is. held securely inthe central aperture I3. (Figure 2) of an insulating disk I4 by meansof a skirt I6 on-the cap I Z-abuttingagainst one sideof the disk.I4 anda ridge I! on the other side of the disk. The periphery of the disk I4 is held iii-a ring I8 of the type-disclosed-in mycopending application, Serial No. 161,-793by means of a plurality of fingers [9 at intervals'aroundthe ring I3; which in turn is welded to thecylindrical sides of the thimble-shapedgrid. 7

The electron-emissive material 22' is located on the top of, the cap, I2Vadjacent the. grid aperture 23. A heater- 24. is held within the cathode sleeve I I by a pair. of supports 25; which in turn are attached by means of a pair of'eyelets 26 to a disk 21, which is secured to the grid by a plurality of fingers 28.

In normal operation, electrical current supplied to the heater 24 heats the cap I2 thereby heating the material 22 sufiiciently to cause the emission of electrons therefrom. These electrons are utilized in the well known way to form a cathode ray beam. In heating the cap I2, the heater 24 also heats the sleeve I I sufiiciently so that over a period of time some of the metal forming the sleeve II will be evaporated, and, will condense on the disk I4, the cooler portion of the zone. In order to provide a break in this metal layer, an annular trough 3|, which i also shown in Figure 2, is cut or molded in the disk I4 during the manufacturing process. The disk I4 must be heat resistant and rigid and is therefore preferably, but not necessarily, made of a ceramic material with one or more breather holes 32 therethrough to assist in evacuating the tube. It is necessary that the side of the trough nearest the cathode be sufficiently perpendicular to the surface of disk I4 so that none of the evaporated metal will see that surface to impinge thereon. Thus a break or shadow in the metal deposition is assured. In order that the ceramic disk I4 may be easily withdrawn from the die in the molding process by which these insulators are usually made, the outer wall 30 of the trough 3| is preferably sloped slightly.

Figure 3 shows the cathode mounted in a different type of insulating disk I I4. Instead of having a trough, the disk H4 has raised portions 33 which may be on both ides in order to provide a leakage-proof surface on the top as Well as the bottom of the disk.

Figures 4 and 5 illustrate two other modifications. In Figure 4 the raised portions 233 are square shaped and may be formed,for instance, by milling the surface :of the disk 2|! in four places around the center. In Figure the slots [3 I are milled into the surface of the disk 3 l 7.

It will be obvious to those skilled in the art that modifications may be made in this invention without departing from the spirit thereof.

What is claimedis: I

1. In a cathode ray tube comprising a tubular electron emitting hot cathode and a tubular cold grid electrode coaxial with and surrounding said cathode, an insulating disk having a surface substantially perpendicular to the axis 'of said tubular electrodes, said disk having a central aperture in which said cathode is secured, the outer periphery of said disk being secured to said tubular portion of said grid, a trough in said disk surrounding said central aperture and intermediate said central aperture and said periphery, the

wall of said trough. nearer to said centralaperture being substantially parallel to the axis of said cathode cylindrical portion and facing said grid. ,2. In a cathode ray tube having a cylindrical cathode andthimble-shaped grid coaxial with andsurrounding said cathode, an insulating disk having a central. aperture in which said cylindriand surrounding said cathode, an insulating disc having a central aperture in which said cylindriwall of said thimble-shaped grid, said disc having a trough in the surfacethereof between said cathode and said grid.

5. In an electron discharge device, a cathodegridassembly comprising an insulating disc having an aperture therein, a cathode positioned in 7 said aperture and securedto said disc, a grid mounted concentrically with said cathode with the outer periphery of said insulating disc being cal cathode coaxially positioned at a point intersecured to the inner wall of said grid, said disc having a trough in the surface thereof between 's'aid'cathode and said grid.

6. In an electron discharge device, a cathodegrid assembly comprising an insulating disc having an aperture therein, a tubular cathode positioned in said aperture and secured to said disc, a tubular grid mounted concentrically with said cathode with the outer periphery of said insulating disc being secured to the inner wall'of said grid, said disc having a'trough in the surface thereof between said cathode and grid.

' ERIC POHLE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name .Date

2,087,327 McNally, July 20, 1937 2,185,807 Gabor etlal Jan. 2, 1940 2,414,500 .West Jan;v 21, 1947 2,440,889 Binneweg, Jr May 4, 1948 2,442,378 Ronci June'1,'l948 2,507,812 Phipps May 16,1959 2,507,979

Kelar May 16, 1950 

